Display screen or a portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or a portion thereof with a graphical user interface, showing our new design.

The broken lines showing a display screen or a portion thereof in all views are for the purpose of illustrating environment and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described. 